Interference noises or unwanted acoustic signals are omnipresent during a conversation between persons. These interfere with the human voice of a person or with a desired acoustic signal. Hearing device wearers are particularly prone to interference noises and unwanted acoustic signals. Conversations in the background, acoustic disturbances from electronic devices, like for instance mobile telephones, as well as noises in the surroundings can make it difficult for a person wearing a hearing device to understand a desired speaker. A reduction in the interference noise level in an acoustic signal, coupled with an automatic focus on a desired acoustic signal component can significantly improve the performance of a digital speech processor, as is used in modern hearing aids.
Hearing devices with a digital signal processing contain one or more microphones, A/D converters, digital signal processors and loudspeakers. Digital signal processors generally divide the incoming signals into a plurality of frequency bands. A signal amplification and processing can be individually adjusted within each band so as to match the requirements of a specific wearer of the hearing device. Furthermore, algorithms for feedback and interference noise minimization are also available in the case of digital signal processing, said algorithms nevertheless also being disadvantageous. The disadvantage with the currently existing algorithms for interference noise minimization is for instance the restricted improvement thereof in terms of the hearing device acoustics, if speech and background noises are in the same frequency range and they are thus not able to distinguish between spoken speech and background noise. This is one of the most frequent aims in the field of acoustic signal processing, namely to filter out one or a plurality of signals from different, superimposing acoustic signals. This is also referred to as the so-called “cocktail party problem”. Here different noises, such as music and chatter, mix to form an indefinable background noise. Nevertheless, it is generally not difficult for a person without a hearing impairment to converse with another person in such a situation. It is thus desirable for hearing device wearers to be able to chat in such situations in a similar way to people without a hearing impairment.
Spatial, e.g. directional microphone or beam forming, statistical, e.g. Blind Source Separation (BSS: “Separation of non visible sound sources”) or mixed methods exist in the acoustic signal processing, which can inter alia separate a single sound source or a plurality thereof from a number of simultaneously active sound sources using algorithms. BSS thus enables a separation of source signals without previous knowledge of their geometric arrangement by means of statistical signal processing of at least two microphone signals. When used in hearing devices, this method is advantageous compared with conventional directional microphone solutions. As a matter of principle, up to n sources can be separated, i.e. n output signals can be generated, using a BSS method with n microphones.
Numerous methods for BSS are known from the literature, with acoustic sources being analyzed by analyzing at least two microphone signals. The subsequently published patent application DE 10 2006 047 982 provides a good overview.
The control of directional microphones within the sense of BSS is subject to ambiguities as soon as several concurrent useful sources, e.g. speakers, are present at the same time. BSS in principle allows the separation of different sources, provided these are spatially separated. The ambiguity nevertheless reduces the potential use of a directional microphone, although a directional microphone can be particularly useful in such scenarios in order to improve speech intelligibility.
The hearing device and/or the mathematical algorithms for BSS have in principle the problem of having to decide which of the signals generated by BSS are to be most advantageously forwarded to the hearing aid wearer. In principle this is an insoluble problem for the hearing aid since the selection of wanted acoustic sources depends directly on the momentary wishes of the hearing aid wearer and a selection algorithm can thus not be present as an input variable. The selection affected by this algorithm must therefore draw upon the assumptions relating to the probable wishes of the hearer.
In the prior art, the hearing aid wearer preferably assumes an acoustic signal from a 0° direction, in other words the line of vision of the hearing aid wearer. This is realistic since the hearing aid wearer would look at his/her current conversational partner in an acoustically difficult situation in order to gain further information in terms of increasing the speech intelligibility of the conversational partner (e.g. lip movements). The hearing aid wearer is however herewith obliged to see his/her conversational partner so that the directional microphone results in increased speech intelligibility. This is particularly inconvenient if the hearing aid wearer wishes to converse with precisely one individual person, i.e. is not included in a communication with several speakers and would not like/have to always see his/her conversational partner.